Underwater Fast Bubble Generating on Pitaya Thorn and Enhanced Biomimetic Gas Collection

Underwater bubble is vital to various applications and many technologies are applied for realizing efficient interfacial bubble generating. Here, the unique underwater bubble generating by the thorn of pitaya is reported. Extensive bubbles are generated underwater within few seconds on the thorn surface. Microbumps and dual-scale ribs grow on the thorn surface, constructing the unique dual-scale groove configuration along the thorn surface. Microbumps equip groove with width gradient. The mechanism of how geometric configuration of groove and surface wettability affect the bubble generating is investigated. Bioinspired study shows that groove configuration can generate bubble within 2 ms by reassembling gas column within groove, which lowers the energy barrier of bubble generating and accelerated gas molecular diffusion toward bubble. Dual-scale groove is beneficial for strengthening surface hydrophobicity and is favorable for reassembling. Besides, width gradient induces the discrepancy of interface curvature along the groove and further accelerates the bubble generating. Accordingly, the dual-scale gradient groove can speed up bubble generating by ≈800%. Especially, the biomimetic combinational groove can realize enhanced underwater gas collection. This research reveals a new mechanism of fast bubble generating which is of great potential for the applications based on underwater bubbles.